Small size datasets for object detection, segmentation and localization
There are various dataset available such as 


Pascal VOC dataset: You can perform all your task with these. 

size of the dataset is as  follows

ADE20K Semantic Segmentation Dataset: you can perform only segmentation here

COCO dataset: This is rich dataset but a size larger then 5 GB so you can try downloading using google colab in your drive and then make a zip file of data as less than 5 GB



You can download all these datasets using Gluoncv easily.here link.